High Speed Protection in A320

[IFLY_INDIGO]

In simulator, flying level with ATHR on, FDs on, AP off, we dived down, sidestick full forward. Airspeed increased, overspeed warning triggered, initially the ROD was about 7000fpm, speed settled at 380 kts and ROD was 4000fpm.
sidestick was maintained full down.

Why high speed protection didn't kick in? there was no malfunction created in the SIM.

[CaptainMongo]

High speed protections:

VMO + 6 knots or MMO + M.01.
Autopilot disconnects
Pitch trim is frozen
Bank angle limit is reduced from 67° to 45°
If no sidestick input is made, the aircraft rolls to wings level.
Sidestick nose-down authority is reduced and a momentary positive pitch-up command is introduced which can be overridden.
If the sidestick is held forward, airspeed will increase further but will stabilize below the design limit speed.
If the sidestick is released,the aircraft continues to pitch-up until the airspeed slows to approximately VMO/MMO at which point the high speed protection is deactivated and normal control laws restored.

[KayPam]

Yes, fully forward stick will allow you to go over VMO/MMO.
Airbus doc says full forward stick will bring you to VD/MD
So about M0.89 and 381kt

[vilas]

The FCOM and FCOM doesn't explain properly the High speed protection. It leaves a doubt whether it supposed only reduce the acceleration or eventually supposed to resume climb even with stick held full forward. FCTM below:

Therefore, in a dive situation:
• If there is no sidestick input on the sidestick, the aircraft will slightly overshoot VMO/MMO and
fly back towards the envelope.
• If the sidestick is maintained full forward, the aircraft will significantly overshoot VMO/MMO without reaching VD/MD. At approximately VMO +16 / MMO +0.04, the pitch nose-down authority smoothly reduces to zero (which does not mean that the aircraft stabilizes at that speed).

The last sentence is ambiguous. It doesn't say it will climb (reduce speed)

[KayPam]

The A/C should stabilize at a speed just below VD/MD (my documents say at VD/MD)
Speed will not reduce to VMO/MMO if you keep pushing fully forward.

[IFLY_INDIGO]

Yes, I found it in sim. Speed settles at 385kts. airplane keep descending, with stick full forward. protection kicked in, only when we released the stick.

[vilas]

From Airbus Safety First
Just some information.

At high altitude, reaching the aircraft’s structural limit Mach number is almost impossible (except in a steep dive with maximum thrust); therefore at high altitude, flying at high Mach number should not be viewed as the biggest threat to the safety of flight.

VMO MMO VD MD
A320 350kt .82M 381kt .89M

[KayPam]

To emphasize this point, I've seen several A/C go more than halfway between MMO and MD being released for service, after the analysis showed that they suffered no structural damage.
(Again, i'm not saying you should try it for fun)